The first section of the proforma is targeted at the clinical picture of the disease. The presenting features will be recorded. The presenting complaints which can be anything ranging from an episode of upper respiratory tract infection to an apparently healthy child presenting with delayed milestones. A brief history of the development milestones achieved under gross motor, fine motor, language and social milestones is important and form a basis for screening the developmentally delayed children .A feeding history will be taken and is important as this disease is more frequently seen in children who are exclusively/predominantly breastfed. A detailed examination of the child would be done and the findings recorded. Skin and hair changes are very classical of this disease and hence will be to be studied and recorded in detail. A neurological examination will be done to study the neurological status of the children and presence of any extrapyramidal symptoms. Hematological indices will be recorded. Plasma Vitamin B 12, folate, homocysteine levels will be studied.Urine methylmalonic acid along with TMS/GCMS will also be done as a part of this project. Other investigations will be done as per case profile. Any other investigation if done for the case as a part of the treatment or diagnostic evaluation like liver function tests, renal function tests , EEG, CT, MRI will also be recorded.